The desirability of hair dye preparations which produce a gradual development of color has long been recognized. Metallic hair dyes have been used for this purpose, but are subject to limitations and disadvantages. Lead dyes are sold commercially for gradual coloring of hair. These use dilute solutions of a lead salt, such as lead acetate or nitrate, and also usually include elemental sulfur. The darkening of the hair is apparently caused by the formation of a complex molecule containing lead and sulfur, either chemically or physically bound to the hair. This system produces only one color--a slightly yellowish black. Brown shades cannot be obtained. Further, the blackish color is produced much more slowly than desirable for most users.
By employing direct dyes, such as nitro dyes, in sufficient dilution, gradual hair coloring can be achieved but it is difficult to control. Further, the user must be careful to avoid discoloration of the hands or skin by contact with the dyes, which have the full color at the time of application. Color produced by such direct dyes is also subject to the disadvantage that it will wash out on shampooing the hair.
The use of oxidative dyes for coloring human hair is also known. However, we are not aware that oxidative dye preparations have heretofore been employed for the gradual coloring of hair. In general, oxidative dye preparations consist of mixtures of ingredients which react in the presence of an oxidizing agent to produce a color. Such dye systems are described in the patent literature. (See, for example, U.S. Pat. Nos. 3,558,259, 3,630,655, 3,647,351 and 3,884,627.) Commonly, they utilize an aromatic diamine or an aromatic aminophenol, or both, in combination with a substituted or unsubstituted mono- or poly-phenol. These preparations are packaged and marketed under oxygen-free conditions and are mixed with an oxidizing agent, usually hydrogen peroxide, immediately prior to application to the hair. Color is thereby rapidly produced, so that the desired shade is normally achieved in a single application. In using and applying such oxidative dye preparations, it is necessary for the user to protect the hands and skin against discoloration.
It is known that oxidative dye preparations will develop color on exposure to atmospheric oxygen. However, as the color reactions occur, different shades or hues result, and the intermediate colors may be quite different than the final color. Consequently, if an attempt is made to use such a preparation for gradual coloration of human hair, such as by repeated applications, the user will have the problem of off-colors during the coloring process. If the treatment extends over several days or longer, as may be desirable, the lack of gradual true color formation would be a serious defect. It is believed that this may be the reason that no one heretofore has proposed the use of an oxidative dye for gradual coloration of human hair.
During the experimental work leading to the present invention, it was discovered that certain specific oxidative dye systems can be successfully employed for the gradual coloring of human hair to a light brown shade. To achieve the development of a gradual true color, with progressive deepening of the shade, it is necessary to utilize the dye components in certain relative proportions. There is no development of "off-color" at any time in the process, either during the actual treatments or in the "aging" periods between applications. The dye system, the required relative proportions, and the method of use will be described below in detail.